The main sign of aging skin in humans is the increased presence of fine lines, deep wrinkles, and sagging skin. These signs of aging are most noticeable on the hands and faces of individuals. Although active agents, such as α-hydroxy acids, β-hydroxy acids and retinoids, are known to combat the underlying causes of wrinkles and fine lines, the prolonged period of time over which administration of these agents is necessary for visible results is inconsistent with the consumer's desire for immediate relief from these signs of aging.
Various film forming agents have been used as tightening and/or tensioning agents. The tightening effect of the film forming agents results from tension on the underlying substrate generated by the film forming agent as it contracts during its drying process. Thus, when the film forming agents are applied to skin the tension is sufficient to draw the skin tight and thereby temporarily smooth fine lines, mitigate deep wrinkles, and lift sagging skin. These tightening agents also have beneficial effects on other human integuments such as eyelashes such that, when applied, the curl of the eyelash is enhanced lifting and improving the eyelash's appearance.
Historically, naturally occurring film forming agents such as albumin derived from egg white or bovine serum have been used. More recently synthetic polymers such as polyvinylpyrrolidone (PVP), polyimides, hydroxyethyl cellulose, polyvinyl alcohol, and acrylate/octylacrylamide copolymer have been used to obtain tightening effects and/or curling effects. However, the tightening and/or curling effects of these above-noted film forming agents are not particularly persistent and are often susceptible to environmental influences such as heat and humidity. For example, under conditions of high humidity compositions containing PVP are known to plasticize, thereby diminishing tension exerted upon the skin.
Accordingly, there is a continuing need in the art for cosmetic compositions that provide a prolonged tightening and/or curling effect substantially resistant to environmental factors such as heat and humidity.
Certain pH-dependent products are known in the art. For example, U.S. Pat. No. 5,993,831 to Ribier et al., incorporated herein by reference in its entirety, is directed to compositions containing nanoparticles of one or more pH-dependent polymers encapsulating an oily phase containing an active agent such as a cosmetic or pharmaceutical. The nanoparticles are said to be from 100 to 1000 nm in diameter, which allows the particles to slip between the outermost corneocytes of the stratum corneum without reaching the living epidermis.
As another example, U.S. Pat. No. 4,976,961 to Norbury et al., incorporated herein by reference in its entirety, is similarly directed to cosmetic emollient oils in microcapsules of pH-dependent polymers. Norbury's microcapsules are said to range in size from 50 to 2000 μm in diameter, and are typically curshed on the skin to release the oils contained therein. The microcapsule shell is said to include organic polymers such as phenolic aldehydes, urea-aldehydes, acrylic polymers, gelatin, and agar.
U.S. Pat. No. 7,053,034 to Shefer et al., incorporated herein by reference in its entirety, is directed to a controlled-release carrier system for targeted delivery of fragrances and active ingredients onto fabric, hair, and skin. Shefer's system is said to include solid hydrophobic nano-spheres encapsulated in a pH or salt sensitive micro-spheres. The micro-spheres are described as having an average sphere size in the range of from about 20 μm (micrometers) to about 100 μm, and the nano-spheres are said to have an average sphere size in the range of from about 0.01 μm to about 5 μm. Moreover, the micro-spheres may be made from such exemplary pH-sensitive materials as copolymers of acrylate polymers with amino substituents, acrylic acid esters, and polyacrylamides. The micro-spheres of Shefer are formed from high temperature melts emulsified into an aqueous phase.
U.S. Patent App. Pub. 2006/0127427 to Vernice et al., incorporated herein by reference in its entirety, describes a surface coated abrasive material, having a water-soluble abrasive core surrounded by a coating that is substantially insoluble in aqueous media during storage but becomes substantially water soluble upon application of substantially large quantities of water or adjustment of the pH of the aqueous medium.
Additionally, European Patents 11806 and 705854 disclose the use of pH-dependent polymers as pH responsive thickening agents.